Method for forming protective film, protective film, and semiconductor process apparatus

Abstract

The present application discloses a method for forming a protective film, a protective film, and a semiconductor process apparatus. The method for forming a protective film comprises depositing a first protective film on an inner wall of a process chamber and depositing a second protective film on a surface of the first protective film, the material of the second protective film being different from the material of the first protective film, and the density of the second protective film being greater than the density of the first protective film, so that the second protective film shows stronger plasma bombardment resistance, thereby effectively reducing the probability of generation of particles from the protective film under plasma bombardment during the process of processing using a PECVD process, further reducing the risk of generation of particle defects on a surface of a wafer. In addition, the smoothness of the second protective film is greater than the smoothness of the first protective film, thereby effectively improving the uniformity of an impedance environment in the process chamber, thereby effectively ensuring the uniformity of plasma distribution in the process chamber during the process of processing using the PECVD process, thus improving intra-wafer and inter-wafer uniformity.

Description

A method for forming a protective film, the protective film, and semiconductor process equipment. Technical Field

[0001] This application relates to the field of semiconductor manufacturing technology, and in particular to a method for forming a protective film, the protective film, and semiconductor process equipment. Background Technology

[0002] PECVD (Plasma Enhanced Chemical Vapor Deposition) is a chemical deposition system that uses glow discharge plasma to dissociate and recombine a gaseous source under low vacuum to grow thin film materials. It has experienced rapid development due to its advantages such as fast deposition speed, low deposition temperature, and support for the deposition of most dielectric films. To prevent metal and particulate contamination during PECVD processing and to provide a stable impedance environment, a protective film is typically formed on the inner wall of the process chamber. However, currently, during PECVD processing, the protective film is highly susceptible to particle generation under plasma bombardment, causing particulate contamination, and the uniformity of the impedance environment within the process chamber cannot be guaranteed. Summary of the Invention

[0003] To address the aforementioned technical problems, this application discloses a method for forming a protective film, the protective film itself, and semiconductor process equipment, thereby resolving the issues in related technologies where the protective film is easily contaminated by particles under plasma bombardment and cannot guarantee the uniformity of the impedance environment in the process chamber.

[0004] To achieve the above technical objectives, the embodiments of this application disclose the following technical solutions:

[0005] In a first aspect, embodiments of this application disclose a method for forming a protective film, comprising: depositing a first protective film on the inner wall of a process chamber; depositing a second protective film on the surface of the first protective film; wherein the material of the second protective film is different from that of the first protective film, and the density and smoothness of the second protective film are greater than those of the first protective film.

[0006] In some embodiments, the second protective film comprises a nitrogen-doped silicon carbide film, and / or the first protective film comprises a silicon oxide film.

[0007] In some embodiments, the thickness of the second protective film is less than the thickness of the first protective film.

[0008] In some embodiments, the thickness of the first protective film is greater than or equal to And / or, the thickness of the second protective film is less than or equal to

[0009] In some embodiments, when depositing a first protective film on the inner wall of the process chamber, a first process gas is introduced into the process chamber. The first process gas includes a first reactive gas and a second reactive gas. The first reactive gas includes a gas containing oxygen, and the second reactive gas includes a gas containing silicon.

[0010] And / or, when depositing a second protective film on the surface of the first protective film, a second process gas is introduced into the process chamber. The second process gas includes a third reaction gas and a fourth reaction gas. The third reaction gas includes a nitrogen-containing gas, and the fourth reaction gas includes a carbon-silicon gas.

[0011] In some embodiments, when the duration of simultaneously introducing the first reactive gas and the second reactive gas into the process chamber reaches a first preset duration, the first radio frequency power supply is turned on to apply the first radio frequency power to the interior of the process chamber.

[0012] And / or, when the duration of simultaneously introducing the third reactant gas and the fourth reactant gas into the process chamber reaches a second preset duration, the first radio frequency power supply and the second radio frequency power supply are controlled to turn on, and the second radio frequency power and the third radio frequency power are respectively applied to the interior of the process chamber, wherein the frequency of the radio frequency signal output by the first radio frequency power supply is higher than the frequency of the radio frequency signal output by the second radio frequency power supply.

[0013] In some embodiments, after the second protective film deposition is completed and before the first RF power supply and the second RF power supply are turned off, the method further includes:

[0014] The first radio frequency power supply is controlled to apply a fourth radio frequency power to the interior of the process chamber, the fourth radio frequency power being less than the second radio frequency power.

[0015] In some embodiments, when the first process gas is introduced into the process chamber, the first reaction gas is introduced into the process chamber, and when a third preset time period is reached, the second reaction gas is introduced into the process chamber.

[0016] And / or, when the second process gas is introduced into the process chamber, the third reaction gas is introduced into the process chamber, and when a fourth preset time period is reached, the fourth reaction gas is introduced into the process chamber.

[0017] Secondly, embodiments of this application disclose a protective film, which includes a first protective film and a second protective film sequentially disposed in the thickness direction of the inner wall of the process chamber;

[0018] The material of the second protective film is different from that of the first protective film, and the density and smoothness of the second protective film are greater than those of the first protective film.

[0019] In some embodiments, the second protective film comprises a nitrogen-doped silicon carbide film, and / or the first protective film comprises a silicon oxide film.

[0020] In some embodiments, the thickness of the second protective film is less than the thickness of the first protective film.

[0021] In some embodiments, the thickness of the first protective film is greater than or equal to And / or, the thickness of the second protective film is less than or equal to

[0022] Thirdly, embodiments of this application disclose a semiconductor process apparatus, including: a process chamber, an inlet assembly, an upper electrode assembly, a lower electrode assembly, and a controller. The controller includes at least one processor and at least one memory, the memory storing a computer program. When the computer program is executed by the processor, it implements the method for forming a protective film as described above.

[0023] Fourthly, embodiments of this specification disclose a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the method for forming a protective film as described above.

[0024] Fifthly, embodiments of this specification disclose a computer program product or computer program, the computer program product including a computer program stored in a computer-readable storage medium; a processor of the computer device reads the computer program from the computer-readable storage medium, and when the processor executes the computer program, it implements the steps of the method for forming a protective film described above.

[0025] The method for forming a protective film, the protective film, and the semiconductor process equipment disclosed in this application deposit a first protective film on the inner wall of a process chamber and a second protective film on the surface of the first protective film. The material of the second protective film is different from that of the first protective film, and the density of the second protective film is greater than that of the first protective film. This gives the protective film stronger resistance to plasma bombardment, thereby effectively reducing the probability of particle formation on the protective film under plasma bombardment during PECVD processing, and thus reducing the risk of particle defects on the wafer surface. At the same time, the smoothness of the second protective film is greater than that of the first protective film, which effectively improves the uniformity of the impedance environment of the process chamber. This ensures the uniformity of plasma distribution within the process chamber during PECVD processing, improving the uniformity within and between wafers. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the published drawings without creative effort.

[0027] Figure 1 is a flowchart illustrating a method for forming a protective film according to one embodiment of this application.

[0028] Figure 2 is a flowchart illustrating another method for forming a protective film disclosed in one embodiment of this application.

[0029] Figure 3 is a schematic diagram comparing the wet etching rates of a nitrogen-doped silicon carbide film deposited according to the method of the present application and a silicon oxide film deposited according to the conventional method.

[0030] Figure 4 shows the trend of the number of particles on the wafer as a function of the cumulative film thickness of the process film.

[0031] Figure 5 is a schematic diagram of the structure of a protective film disclosed in one embodiment of this application.

[0032] Figure 6 is a schematic diagram of the structure of a semiconductor process apparatus disclosed in one embodiment of this application. Detailed Implementation

[0033] Unless otherwise defined, the technical or scientific terms used in the embodiments of this specification shall have the ordinary meaning understood by one of ordinary skill in the art to which this specification pertains. The terms "first," "second," and similar terms used in the embodiments of this specification do not indicate any order, quantity, or importance, but are merely used to avoid confusion of constituent elements.

[0034] Unless the context otherwise requires, throughout this specification, "a plurality of" means "at least two," and "including" is interpreted as open-ended or encompassing, that is, "including, but not limited to." In the description of this specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this specification. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example.

[0035] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this specification.

[0036] Currently, performance improvements in computing and storage devices rely on the high integration of chip manufacturing. However, with the miniaturization of devices and the continuous increase in stacked film layers, higher demands are placed on the repeatability, stability, and control of defects and in-film particle counts at each process stage. Furthermore, high-quality thin-film deposition capabilities limit wafer manufacturing throughput to some extent, thus requiring greater optimization of thin-film deposition processes.

[0037] As mentioned in the background section, PECVD is a relatively mature chemical deposition system. It utilizes glow discharge plasma to dissociate and recombine gaseous sources under low vacuum to achieve the growth of thin film materials. PECVD has advantages such as fast deposition speed, low deposition temperature, and support for the deposition of most dielectric thin films, including etch stop layers (ESL), hard masks (HM), inter-metal dielectric layers (IMD), and inter-layer dielectric layers (ILD) for semiconductor devices. Therefore, it has developed rapidly and has wide applications in fields such as ultra-large-scale integrated circuits, optoelectronic devices, and MEMS (Micro-Electro-Mechanical Systems).

[0038] To prevent metal and particulate contamination during PECVD processing and to provide a stable impedance environment, a protective film, or pre-coating layer, is typically formed on the inner wall of the process chamber. This protective film covers the metal inner wall of the process chamber, preventing it from peeling off under plasma bombardment and causing metal contamination. Simultaneously, the protective film serves as an intermediate adhesion layer to prevent the deposited process film from peeling off the inner wall of the process chamber during PECVD processing, thus avoiding particulate contamination. Furthermore, the protective film acts as a dielectric layer, balancing the internal impedance of the process chamber to provide a stable impedance environment and improve the stability of film deposition. For example, when the number of deposited process films in the process chamber reaches a predetermined quantity or the film thickness on the inner wall of the process chamber reaches a preset thickness, a remote plasma source (RPS) cleaning is performed to remove the accumulated film on the inner wall of the chamber. A protective film is then deposited on the inner wall of the process chamber before the next film deposition.

[0039] Currently, during the deposition of protective films on the inner wall of process chambers, only one layer of film is typically deposited, such as a silicon oxide (SiO2) film. Silicon oxide is a common pre-coating material and a commonly used dielectric layer. Its preparation process is mature, its uniformity is relatively easy to control, and it has good adhesion to the inner wall of aluminum process chambers. At the same time, using PECVD can obtain a thicker silicon oxide film in a shorter time, which is beneficial to improving equipment capacity.

[0040] However, silicon oxide films have low density and are easily bombarded by plasma during PECVD processes, especially in high-power deposition processes, resulting in particle contamination. Furthermore, the non-uniformity and roughness of the silicon oxide film surface can affect the uniformity of the impedance environment within the process chamber, thus making it impossible to guarantee uniformity within and between wafers during PECVD processes.

[0041] In addition, although adjusting the process parameters during the deposition of silicon oxide film can improve the density of silicon oxide film to a certain extent and thus reduce particulate contamination during the PECVD process, it still cannot meet the requirements for wafer processing quality.

[0042] Therefore, it is necessary to disclose a method for forming a protective film to effectively reduce the risk of particulate contamination caused by the protective film under plasma bombardment and to improve the uniformity of the impedance environment of the process chamber.

[0043] To address the problems of traditional protective films being easily contaminated by particles under plasma bombardment and failing to guarantee the uniformity of the impedance environment in the process chamber, the technical solution disclosed in this application involves depositing a first protective film on the inner wall of the process chamber and a second protective film on the surface of the first protective film. The second protective film is made of a different material than the first protective film, and its density is greater than that of the first protective film. This gives the protective film stronger resistance to plasma bombardment, effectively reducing the probability of particles forming on the protective film under plasma bombardment during PECVD processing, thereby reducing the risk of particle defects on the wafer surface. Simultaneously, the smoothness of the second protective film is greater than that of the first protective film, effectively improving the uniformity of the impedance environment in the process chamber. This, in turn, ensures the uniformity of plasma distribution within the process chamber during PECVD processing, improving the uniformity both within and between wafers.

[0044] In addition, the method for forming a protective film disclosed in the embodiments of this application has improved the process parameters in the deposition process of the first and second protective films.

[0045] As one implementation of the disclosure in this application, an embodiment of this application discloses a method for forming a protective film, as shown in FIG1, including the following steps:

[0046] S101. Deposit a first protective film on the inner wall of the process chamber.

[0047] Specifically, the process chamber can be a chamber used to perform PECVD process processing, which includes, but is not limited to, the deposition of silicon oxide-doped dielectric films, silicon carbide-doped dielectric films, silicon nitride-doped dielectric films, and silicon-based low-k dielectric films.

[0048] The inner wall of the process chamber may include each inner wall of the process chamber. The material of the first protective film may be a material with good adhesion to the inner wall of the process chamber to reduce the risk of the first protective film peeling off during the PECVD process. For example, the first protective film may include a silicon oxide film.

[0049] During the deposition of the first protective film on the inner wall of the process chamber, a first process gas can be introduced into the process chamber, and a first target RF power supply can be turned on to deposit the first protective film. Once the deposition of the first protective film is complete, the first target RF power supply can be turned off, the introduction of the first process gas into the process chamber can be stopped, and the process chamber can be evacuated. The first process gas may include a reactive gas used to obtain the first protective film, and may also include an inert gas. The first target RF power supply may include a first RF power supply, and may also include both a first RF power supply and a second RF power supply. The frequency of the RF signal output by the first RF power supply may be higher than the frequency of the RF signal output by the second RF power supply; for example, the first RF power supply may be a high-frequency RF power supply, and the second RF power supply may be a low-frequency RF power supply.

[0050] S102, depositing a second protective film on the surface of the first protective film; wherein the material of the second protective film is different from that of the first protective film, and the density and smoothness of the second protective film are greater than those of the first protective film.

[0051] Specifically, when the first protective film is deposited, a second protective film can be further deposited on the surface of the first protective film. That is, the second protective film adheres to the inner wall of the process chamber through the first protective film to form a pre-coating layer together with the first protective film. In other words, the pre-coating layer on the inner wall of the process chamber includes the first protective film and the second protective film. During the PECVD process in the process chamber, the surface of the second protective film can be in direct contact with the internal environment of the process chamber.

[0052] The material of the second protective film can be different from that of the first protective film. It should be noted that the material of the second protective film can be a material that has good adhesion to the first protective film, so that the second protective film and the first protective film have strong adhesion, thereby reducing the risk of the first protective film and the second protective film peeling off during the PECVD process.

[0053] During the deposition of the second protective film on the surface of the first protective film, a second process gas can be introduced into the process chamber, and the second target RF power supply can be turned on to deposit the second protective film. When the deposition of the second protective film is complete, the second target RF power supply can be turned off, the introduction of the second process gas into the process chamber can be stopped, and the process chamber can be evacuated. The second process gas may include a reactive gas used to obtain the second protective film, and may also include an inert gas. The second target RF power supply may include a first RF power supply, or may include both a first RF power supply and a second RF power supply simultaneously.

[0054] The density of the second protective film can be greater than that of the first protective film. That is, the second protective film has stronger resistance to plasma bombardment than the first protective film. Therefore, during the PECVD process, the second protective film can effectively reduce the probability of particles being generated on the protective film under plasma bombardment, thereby reducing the risk of particle defects on the wafer surface.

[0055] Meanwhile, the smoothness of the second protective film can be greater than that of the first protective film. That is, the surface of the pre-coated layer on the inner wall of the process chamber that comes into contact with the internal environment of the process chamber is smoother, and the roughness and non-uniformity are effectively reduced. This can effectively improve the uniformity of the impedance environment of the process chamber. Thus, during the PECVD process, the second protective film can effectively ensure the uniformity of plasma distribution in the process chamber, thereby improving the uniformity within and between wafers.

[0056] Currently, the inner wall of the process chamber is typically deposited with a single layer of silicon oxide film. However, this single layer of silicon oxide film has poor adhesion to the process films (e.g., silicon carbide-doped dielectric films) deposited during PECVD processing. Therefore, the process films deposited during PECVD processing are prone to peeling off from the inner wall of the process chamber, causing particulate contamination. To avoid particulate contamination caused by the peeling off of the process films from the inner wall of the process chamber, it is usually necessary to reduce the cumulative thickness of the process films between RPS cleaning intervals. The cumulative thickness of the process films is the total thickness of the process films deposited on the inner wall of the process chamber between two adjacent RPS cleaning intervals. This results in a significant increase in the RPS cleaning frequency. Since each RPS cleaning requires a shutdown, the increased RPS cleaning frequency leads to a significant increase in downtime maintenance, making it impossible to guarantee wafer manufacturing capacity. To reduce the RPS cleaning frequency of the process chamber, in one embodiment of this specification, the second protective film includes a nitrogen-doped silicon carbide film, and / or the first protective film includes a silicon oxide film.

[0057] Specifically, nitrogen-doped silicon carbide films have similar atomic compositions and better stress matching to process films deposited during PECVD processing. Process films include, but are not limited to, silicon oxide-doped dielectric films, silicon carbide-doped dielectric films, silicon nitride-doped dielectric films, and silicon-based low-k dielectric films, thereby enhancing the adhesion between nitrogen-doped silicon carbide films and process films deposited during PECVD processing.

[0058] Meanwhile, the nitrogen-doped silicon carbide film and the silicon oxide film have good adhesion, and the silicon oxide film also has good adhesion to the metal inner wall of the process chamber. In other words, the silicon oxide film plays an excellent intermediate adhesion role between the nitrogen-doped silicon carbide film and the metal inner wall of the process chamber. This reduces the risk of peeling of the nitrogen-doped silicon carbide film from the metal inner wall of the process chamber during the PECVD process. Through the synergistic effect of the nitrogen-doped silicon carbide film and the silicon oxide film, the process chamber can still avoid particles generated by peeling of the process film even with a large cumulative film thickness. This effectively reduces the RPS cleaning frequency and improves the wafer manufacturing capacity.

[0059] In addition, nitrogen-doped silicon carbide films have better density and smoothness, thus having stronger resistance to plasma bombardment. During PECVD processing, they can effectively reduce the probability of particles being generated in the protective film under plasma bombardment, and can effectively improve the uniformity of the impedance environment in the process chamber. This further reduces the risk of particle defects on the wafer surface and improves the uniformity of plasma distribution in the process chamber.

[0060] In some embodiments of this application, the thickness of the second protective film is less than the thickness of the first protective film.

[0061] Specifically, the thickness of the second protective film can be less than the thickness of the first protective film. For example, the thickness of the first protective film can be greater than or equal to the first preset thickness, the thickness of the second protective film can be less than or equal to the second preset thickness, and the first preset thickness can be greater than the second preset thickness.

[0062] Since the density and smoothness of the second protective film are greater than those of the first protective film, the deposition rate of the second protective film is lower than that of the first protective film. By setting the thickness of the second protective film to be less than that of the first protective film, the deposition time of the pre-coated layer on the inner wall of the process chamber can be effectively shortened.

[0063] Meanwhile, by setting the thickness of the first protective film to be greater than or equal to the first preset thickness, the total thickness of the pre-coated layer on the inner wall of the process chamber can be effectively guaranteed. Thus, during the PECVD process, the thicker pre-coated layer can effectively balance the impedance in the process chamber, thereby providing a stable impedance environment for the process chamber, improving the uniformity of plasma distribution, and further improving the stability of thin film deposition during the PECVD process.

[0064] Therefore, by setting the thickness of the second protective film to be less than that of the first protective film, the deposition time of the pre-coated layer on the inner wall of the process chamber can be shortened while effectively improving the stability of the impedance environment of the process chamber.

[0065] In some embodiments of this application, the thickness of the first protective film is greater than or equal to And / or, the thickness of the second protective film is less than or equal to

[0066] Specifically, the thickness of the first protective film can be greater than or equal to A thicker first protective film can effectively balance the impedance within the process chamber, thereby providing a stable impedance environment for the process chamber, improving the uniformity of plasma distribution, and further enhancing the stability of thin film deposition during PECVD processing.

[0067] In addition, the thickness of the second protective film can be less than or equal to On the one hand, the second protective film, due to its better density and smoothness, possesses stronger resistance to plasma bombardment. This effectively reduces the probability of particle formation on the protective film under plasma bombardment during PECVD processing and significantly improves the uniformity of the impedance environment within the process chamber. Consequently, it lowers the risk of particle defects on the wafer surface and enhances the uniformity of plasma distribution within the process chamber. On the other hand, it effectively shortens the deposition time of the second protective film, thereby improving the deposition efficiency of the pre-coated layer on the inner wall of the process chamber.

[0068] In some embodiments of this application, when depositing a first protective film on the inner wall of the process chamber, a first process gas is introduced into the process chamber. The first process gas includes a first reactive gas and a second reactive gas. The first reactive gas includes a gas containing oxygen, and the second reactive gas includes a gas containing silicon. And / or, when depositing a second protective film on the surface of the first protective film, a second process gas is introduced into the process chamber. The second process gas includes a third reactive gas and a fourth reactive gas. The third reactive gas includes a gas containing nitrogen, and the fourth reactive gas includes a gas containing carbon and silicon elements.

[0069] Specifically, the first process gas may include a first reactant gas and a second reactant gas, which can be used to react and generate a first protective film. For example, the first reactant gas may include oxygen-containing gases, such as nitrous oxide (N2O), oxygen (O2), carbon dioxide (CO2), etc., and the second reactant gas may include silicon-containing gases, such as silane (SiH4). For instance, the first reactant gas can be nitrous oxide, which readily reacts with silane and produces fewer byproducts, effectively ensuring the stability of the components of the first protective film and thus improving the film-forming quality of the first protective film.

[0070] In practice, the process chamber may include an inlet assembly. When depositing the first protective film on the inner wall of the process chamber, a first process gas can be introduced into the process chamber through the inlet assembly. The first reactant gas and the second reactant gas in the first process gas can react in a plasma state to achieve the deposition of the first protective film. The flow rate of the first reactant gas can be in the range of 100–30000 sccm, and the flow rate of the second reactant gas can be in the range of 100–5000 sccm.

[0071] The second process gas may include a third reactant gas and a fourth reactant gas, which can be used to react and generate a second protective film. For example, the third reactant gas may include a nitrogen-containing gas, such as ammonia (NH3), and the fourth reactant gas may include a carbon-silicon gas, such as tetramethylsilane (Si(CH3)4) or trimethylsilane (C3H2O). 10 Si), etc. For example, the fourth reactant gas can be tetramethylsilane, which readily reacts with ammonia and produces few byproducts, effectively ensuring the stability of the components of the second protective film and thus improving the film-forming quality of the second protective film.

[0072] In practice, when depositing the second protective film on the surface of the first protective film, a second process gas can be introduced into the process chamber through the gas inlet assembly. The third and fourth reactant gases in the second process gas can react in a plasma state to achieve the deposition of the second protective film. The flow rate of the third reactant gas can be in the range of 1000–10000 sccm, and the flow rate of the fourth reactant gas can be in the range of 100–10000 sccm.

[0073] It is understood that the first process gas and / or the second process gas may also include inert gases, such as nitrogen (N2), helium (He), argon (Ar), etc. For example, nitrogen may be used as the inert gas. The inert gas does not react during the deposition of the first protective film and / or the second protective film, and by introducing inert gas into the process chamber, the reactant gases in the first process gas and / or the second process gas can be uniformly distributed inside the process chamber, effectively improving the uniformity of film formation.

[0074] Specifically, when depositing the first protective film on the inner wall of the process chamber, the inert gas flow rate can be in the range of 1000 to 5000 sccm; when depositing the second protective film on the surface of the first protective film, the inert gas flow rate can be in the range of 1000 to 10000 sccm.

[0075] To further improve the deposition rate of the first and second protective films, in some embodiments of this application, when the duration of simultaneously introducing the first and second reactive gases into the process chamber reaches a first preset duration, the first radio frequency power supply is turned on to apply the first radio frequency power to the interior of the process chamber; and / or, when the duration of simultaneously introducing the third and fourth reactive gases into the process chamber reaches a second preset duration, the first and second radio frequency power supplies are turned on to apply the second and third radio frequency power to the interior of the process chamber, respectively, wherein the frequency of the radio frequency signal output by the first radio frequency power supply is higher than the frequency of the radio frequency signal output by the second radio frequency power supply.

[0076] Specifically, during the deposition of the first protective film on the inner wall of the process chamber, when the duration of simultaneous introduction of the first and second reactive gases into the process chamber reaches a first preset duration, the first radio frequency power supply can be turned on. By turning on the first radio frequency power supply, a high-frequency radio frequency field can be applied inside the process chamber to provide energy through the high-frequency radio frequency field to excite the reactive gas corresponding to the first protective film to dissociate into gas molecules.

[0077] The first preset duration can be in the range of 1 to 5 seconds, so that the first reactant gas and the second reactant gas inside the process chamber are evenly distributed before the first radio frequency power supply is turned on, which further improves the uniformity of the first protective film formation.

[0078] In practice, the radio frequency power of the first radio frequency power supply can be adjusted to the first radio frequency power. The first radio frequency power can be determined based on the first target deposition rate of the first protective film. For example, for different reactive gases, a correspondence between the first radio frequency power and the first target deposition rate can be set. Based on the reactive gas corresponding to the first protective film and the first target deposition rate of the first protective film, the first radio frequency power of the first radio frequency power supply can be determined. Then, by controlling the first radio frequency power supply to turn on and apply the first radio frequency power to the inside of the process chamber, the deposition rate of the first protective film can be effectively accelerated.

[0079] Furthermore, during the deposition of the second protective film on the first protective film, when the duration of simultaneous introduction of the third and fourth reactive gases into the process chamber reaches a second preset duration, the first and second radio frequency (RF) power supplies can be simultaneously activated. The frequency of the RF signal output by the first RF power supply is higher than the frequency of the RF signal output by the second RF power supply. By activating the first RF power supply, a high-frequency RF field can be applied inside the process chamber to provide energy for the reactive gas corresponding to the second protective film to dissociate into gas molecules. By activating the second RF power supply, a low-frequency RF field can be applied inside the process chamber to provide energy for the dissociated gas molecules to recombine, thereby effectively increasing the recombination probability of the dissociated gas molecules and thus improving the film formation rate of the second protective film.

[0080] The second preset duration can be in the range of 1 to 60 seconds, so that the third and fourth reactant gases inside the process chamber are evenly distributed before the first and second radio frequency power supplies are turned on, which further improves the uniformity of the second protective film formation.

[0081] In practice, the RF power of the first RF power supply can be adjusted to the second RF power and the RF power of the second RF power supply can be adjusted to the third RF power. The second RF power and the third RF power can be determined based on the second target deposition rate of the second protective film. For example, for different reactive gases, the correspondence between the second RF power and the third RF power and the second target deposition rate can be set. Based on the reactive gas corresponding to the second protective film and the second target deposition rate of the second protective film, the second RF power of the first RF power supply and the third RF power of the second RF power supply can be determined. Then, by controlling the first RF power supply and the second RF power supply to turn on and apply the second RF power and the third RF power to the inside of the process chamber respectively, the deposition rate of the second protective film can be effectively accelerated.

[0082] Understandably, a spray assembly and a wafer carrier can be installed inside the process chamber. The spray assembly is used to uniformly distribute the process gas entering the process chamber, and the first and second RF power supplies can provide RF power through the spray assembly. The wafer carrier can be grounded, and when the first and / or second RF power supplies are turned on, a bias voltage can be generated between the spray assembly and the wafer carrier. This bias voltage can effectively increase the mean free path of the dissociated gas molecules, further improving the deposition rate of the first and second protective films.

[0083] In some embodiments of this application, after the second protective film deposition is completed and before the first and second RF power supplies are turned off, the method further includes: controlling the first RF power supply to apply a fourth RF power to the interior of the process chamber, the fourth RF power being less than the second RF power.

[0084] Specifically, during the deposition of the second protective film, the deposition time of the second protective film can be monitored in real time. The deposition time of the second protective film may include the on-time of the first radio frequency power supply and / or the second radio frequency power supply. When the deposition time of the second protective film reaches the preset deposition time, the deposition of the second protective film is determined to be completed.

[0085] When the second protective film deposition is completed, the output power of the first radio frequency power supply can be adjusted. For example, the first radio frequency power supply can be controlled to apply a fourth radio frequency power to the inside of the process chamber. The fourth radio frequency power can be less than the second radio frequency power to reduce the output power of the first radio frequency power supply.

[0086] By reducing the output power of the first radio frequency power supply, the dissociation rate of the reactive gas corresponding to the second protective film can be effectively reduced, allowing the dissociated gas molecules in the process chamber to fully recombine. At the same time, by continuously applying radio frequency power to the interior of the process chamber through the first radio frequency power supply, the dissociated gas molecules in the process chamber can be kept in a suspended state. This avoids the unrecombined gas molecules falling and generating particles that would affect the smoothness and density of the second protective film if the first radio frequency power supply is turned off directly at the end of the deposition of the second protective film, thus effectively improving the film quality of the second protective film.

[0087] It is understandable that after the second protective film deposition is completed and before the first and second RF power supplies are turned off, the second RF power supply can be controlled to apply a fifth RF power to the interior of the process chamber. The fifth RF power can be less than the third RF power in order to reduce the output power of the second RF power supply.

[0088] Before shutting down the first and second RF power supplies, reducing their output power allows for a gradual withdrawal of the RF field from the process chamber. This effectively prevents abrupt changes in plasma conditions within the process chamber caused by the direct shutdown of the first and second RF power supplies, such as temperature and stress. Consequently, it avoids reduced density and cracks in the second protective film due to abrupt changes in plasma conditions, thus ensuring the quality of the second protective film.

[0089] In some embodiments of this application, the second radio frequency power ranges from 100 to 2000W, and / or the third radio frequency power ranges from 100 to 2000W.

[0090] Specifically, the range of the second radio frequency power can be 100–2000W (inclusive), and the range of the third radio frequency power can be 100–2000W (inclusive). In practice, the magnitudes of the second and third radio frequency powers can be determined based on the film formation quality requirements (e.g., particle condition of the second protective film) and the film formation rate requirements of the second protective film.

[0091] It is understandable that the range of the fourth RF power can be the same as the range of the second RF power, and the fourth RF power is less than the second RF power; in addition, the range of the fifth RF power can be the same as the range of the third RF power, and the fifth RF power is less than the third RF power.

[0092] In addition, the range of the first radio frequency power can be 100 to 2000W (including the endpoint value). In practice, the magnitude of the first radio frequency power can be determined based on the film formation quality requirements of the first protective film (e.g., the particle condition of the first protective film).

[0093] In order to further improve the uniformity of the first protective film and / or the second protective film, in one embodiment of this specification, when the first process gas is introduced into the process chamber, a first reaction gas is also introduced into the process chamber, and when a third preset time is reached, the second reaction gas is introduced into the process chamber.

[0094] And / or, while the second process gas is introduced into the process chamber, a third reaction gas is also introduced into the process chamber, and when a fourth preset time is reached, a fourth reaction gas is introduced into the process chamber.

[0095] Specifically, when introducing the first process gas into the process chamber, a first reactive gas and an inert gas can be introduced first to ensure that the first reactive gas is evenly distributed inside the process chamber. After a third preset time period, the second reactive gas is introduced into the process chamber. That is, after the third preset time period, the first reactive gas, the inert gas, and the second reactive gas are introduced into the process chamber simultaneously. Thus, by introducing the second reactive gas after the first reactive gas is evenly distributed inside the process chamber, the uniformity of the first protective film can be effectively guaranteed.

[0096] In practice, during the deposition of the first protective film on the inner wall of the process chamber, a first reactive gas and an inert gas can be introduced into the process chamber first. After a third preset time is reached, a second reactive gas is introduced into the process chamber. After the time for introducing the second reactive gas reaches the first preset time, the first radio frequency power supply is turned on to deposit the first protective film, thereby further improving the uniformity of the first protective film.

[0097] When introducing the second process gas into the process chamber, the third reactant gas and the inert gas can be introduced first to ensure that the third reactant gas is evenly distributed inside the process chamber. After a fourth preset time period, the fourth reactant gas is introduced into the process chamber simultaneously. That is, after the fourth preset time period, the third reactant gas, the inert gas, and the fourth reactant gas are introduced into the process chamber simultaneously. Therefore, by introducing the fourth reactant gas after the third reactant gas is evenly distributed inside the process chamber, the uniformity of the second protective film can be effectively guaranteed.

[0098] In practice, during the deposition of the second protective film on the surface of the first protective film, a third reactive gas and an inert gas can be introduced into the process chamber first. After a fourth preset time is reached, a fourth reactive gas is introduced into the process chamber. After the time for introducing the fourth reactive gas reaches the second preset time, the first and second radio frequency power supplies are turned on to deposit the second protective film, which further improves the uniformity of the second protective film.

[0099] The following describes an optional implementation method for forming a protective film according to this application. As shown in Figure 2, the method includes the following steps:

[0100] S201. Inert gas nitrogen and first reactant gas nitrous oxide are introduced into the process chamber to mix and control the pressure before the first protective film is deposited. In this step, the flow rate of nitrogen is in the range of 1000 to 5000 sccm; the flow rate of nitrous oxide is in the range of 100 to 30000 sccm; the pressure control range is 0.1 to 10 torr; and the execution time of this step is in the range of 1 to 60 seconds.

[0101] S202. Introduce the second reactive gas, silane, into the process chamber to mix and control the pressure of all reactive gases, including silane, before the deposition of the first protective film. In this step, the gas flow rate of silane ranges from 100 to 5000 sccm; the gas flow rate of nitrogen ranges from 1000 to 5000 sccm; the gas flow rate of nitrous oxide ranges from 100 to 30000 sccm; the pressure control ranges from 0.1 to 10 torr; and the execution time of this step ranges from 1 to 5 seconds.

[0102] S203. Control the first radio frequency power supply to turn on, and apply the first radio frequency power to the interior of the process chamber to deposit a first protective film on the inner wall of the process chamber; in this step, the range of the first radio frequency power is 100 to 2000W; the range of the silane gas flow rate is 100 to 5000 sccm; the range of the nitrogen gas flow rate is 1000 to 5000 sccm; the range of the nitrous oxide gas flow rate is 100 to 30000 sccm; the range of the pressure control is 0.1 to 10 torr; the execution duration of this step is 10 to 600 seconds.

[0103] S204. Stop the introduction of the second reactive gas silane into the process chamber to stop the deposition of the first protective film. In this step, the gas flow rate of nitrogen, the gas flow rate of nitrous oxide, and the first radio frequency power remain unchanged compared to step S203. Only the introduction of the second reactive gas silane into the process chamber is stopped.

[0104] S205, control the first radio frequency power supply to turn off, stop the supply of inert gas nitrogen and first reactive gas nitrous oxide to the process chamber, and control the process chamber to be evacuated.

[0105] S206. Inert gas nitrogen and third reactive gas ammonia are introduced into the process chamber to mix and control the pressure before the second protective film is deposited. In this step, the flow rate of nitrogen is in the range of 1000 to 10000 sccm; the flow rate of ammonia is in the range of 1000 to 10000 sccm; the pressure control range is 0.1 to 10 torr; and the execution time of this step is in the range of 1 to 60 seconds.

[0106] S207. Introduce the fourth reactive gas, tetramethylsilane, into the process chamber to mix and control the pressure of all reactive gases, including tetramethylsilane, before the deposition of the second protective film. In this step, the gas flow rate of tetramethylsilane ranges from 100 to 10000 sccm; the gas flow rate of nitrogen ranges from 1000 to 10000 sccm; the gas flow rate of ammonia ranges from 1000 to 10000 sccm; the pressure control ranges from 0.1 to 10 torr; and the execution time of this step ranges from 1 to 60 seconds.

[0107] S208. Control the first and second radio frequency power supplies to turn on, and apply the second and third radio frequency power to the interior of the process chamber, respectively, to deposit a second protective film on the inner wall of the process chamber; in this step, the range of the second radio frequency power is 100-2000W, the range of the third radio frequency power is 100-2000W; the range of the tetramethylsilane gas flow rate is 100-10000sccm; the range of the nitrogen gas flow rate is 1000-10000sccm; the range of the ammonia gas flow rate is 1000-10000sccm; the pressure control range is 0.1-10 torr; the execution duration of this step ranges from 1 to 600 seconds.

[0108] S209. Adjust the output power of the first and second RF power supplies, and apply the fourth and fifth RF power to the interior of the process chamber, respectively, to prepare for shutting down the first and second RF power supplies. In this step, the fourth RF power ranges from 100 to 2000 W, the fifth RF power ranges from 100 to 2000 W, the fourth RF power is less than the second RF power, and the fifth RF power is less than the third RF power; the flow rate of tetramethylsilane gas ranges from 100 to 10000 sccm; the flow rate of nitrogen gas ranges from 1000 to 10000 sccm; the flow rate of ammonia gas ranges from 1000 to 10000 sccm; the pressure control range is 0.1 to 10 torr; the execution time of this step ranges from 1 to 60 seconds.

[0109] S210, turn off the first RF power supply and the second RF power supply, and stop the supply of inert gas nitrogen, third reactant gas ammonia and fourth reactant gas tetramethylsilane to the process chamber, and control the process chamber to be evacuated.

[0110] The beneficial effects of the method for forming the protective film in this embodiment are verified through experiments below.

[0111] Wet Etch Rate (WER) Verification: Four sets of samples were prepared. Each set of samples included a nitrogen-doped silicon carbide film deposited on a bare silicon wafer according to the method of this embodiment, and a silicon oxide film deposited on a bare silicon wafer according to a conventional method. The four sets of samples were wet etched in a 100:1 hydrofluoric acid solution. The comparison of the wet etch rates of the nitrogen-doped silicon carbide film and the silicon oxide film is shown in Figure 3. As can be seen from Figure 3, the wet etch rate of the nitrogen-doped silicon carbide film is much smaller than that of the silicon oxide film. It can be seen that the nitrogen-doped silicon carbide film deposited according to the method of this embodiment has higher density and etching resistance than the silicon oxide film deposited according to the conventional method. Therefore, by depositing a nitrogen-doped silicon carbide film on the surface of the first protective film in the process chamber, the probability of particle generation of the nitrogen-doped silicon carbide film under plasma bombardment can be effectively reduced during the process, thereby reducing the risk of particle defects on the wafer surface.

[0112] Wafer particle contamination verification: Based on the method of this embodiment, a first protective film is deposited on the inner wall of the process chamber and a second protective film is deposited on the surface of the first protective film. During PECVD processing in the process chamber, the cumulative film thickness of the process films is statistically analyzed. Growth to The number of particles larger than 0.4 μm on the wafer during the process is statistically analyzed, and the results are shown in Figure 4. As can be seen from Figure 4, the number of particles on the wafer did not increase significantly with the increase in the cumulative thickness of the process film. This indicates that the protective film prepared by the method in this embodiment has a good inhibitory effect on wafer particle contamination. The second protective film acts as an excellent intermediate adhesion layer between the first protective film and the process film, and effectively increases the cumulative thickness of the process film during the RPS cleaning interval, thereby improving the wafer manufacturing throughput.

[0113] As another implementation of the disclosure of this application, this application embodiment also discloses a protective film. Referring to FIG5, the protective film 300 includes a first protective film 301 and a second protective film 302 sequentially disposed in the thickness direction of the inner wall of the process chamber 20; wherein, the material of the second protective film 302 is different from that of the first protective film 301, and the density and smoothness of the second protective film 302 are greater than those of the first protective film 301. That is, the second protective film 302 adheres to the inner wall of the process chamber 20 through the first protective film 301. During the PECVD process in the process chamber 20, the surface of the second protective film 302 can directly contact the internal environment of the process chamber 20. By setting the density of the second protective film 302 to be greater than that of the first protective film 301, the second protective film 302 has a stronger resistance to plasma bombardment than the first protective film 301. Thus, during the PECVD process, the probability of particles being generated on the protective film 300 under plasma bombardment can be effectively reduced, thereby reducing the risk of particle defects on the wafer surface. Meanwhile, by setting the smoothness of the second protective film 302 to be greater than that of the first protective film 301, the surface of the protective film 300 in contact with the internal environment of the process chamber 20 is smoother, and the roughness and non-uniformity are effectively reduced. This effectively improves the uniformity of the impedance environment of the process chamber 20. Thus, during the PECVD process, the uniformity of plasma distribution in the process chamber 20 can be effectively guaranteed, thereby improving the uniformity within and between wafers.

[0114] For example, the second protective film 302 includes a nitrogen-doped silicon carbide film, and / or the first protective film 301 includes a silicon oxide film. The nitrogen-doped silicon carbide film has an atomic composition similar to that of the process film deposited during the PECVD process and a better stress match, which enhances the adhesion between the second protective film 302 and the process film deposited during the PECVD process. At the same time, the nitrogen-doped silicon carbide film has good adhesion to the silicon oxide film, and the silicon oxide film has good adhesion to the metal inner wall of the process chamber 20. Thus, through the synergistic effect of the first protective film 301 and the second protective film 302, the process chamber 20 can be protected from particles generated by the peeling of the process film even with a large cumulative film thickness during the PECVD process, thereby effectively reducing the RPS cleaning frequency and improving the wafer manufacturing capacity. In addition, nitrogen-doped silicon carbide films have better density and smoothness, thus having stronger resistance to plasma bombardment. This effectively reduces the probability of particles forming on the protective film under plasma bombardment during PECVD processing and effectively improves the uniformity of the impedance environment in the process chamber 20. This further reduces the risk of particle defects on the wafer surface and improves the uniformity of plasma distribution within the process chamber 20.

[0115] For example, the thickness of the second protective film 302 is less than the thickness of the first protective film 301, which can effectively shorten the deposition time of the protective film 300 on the inner wall of the process chamber 20. At the same time, it can ensure the overall thickness of the protective film 300, so that the protective film 300 can effectively balance the impedance in the process chamber 20, thereby providing a stable impedance environment for the process chamber 20, improving the uniformity of plasma distribution, and further improving the stability of thin film deposition during the PECVD process.

[0116] For example, the thickness of the first protective film 301 is greater than or equal to And / or, the thickness of the second protective film 302 is less than or equal to By setting a thicker first protective film 301, the impedance within the process chamber 20 can be effectively balanced, thereby providing a stable impedance environment for the process chamber 20 and improving the uniformity of plasma distribution, which in turn further improves the stability of thin film deposition during the PECVD process. At the same time, by setting a thinner second protective film 302, the deposition time of the second protective film 302 can be effectively shortened, thereby improving the deposition efficiency of the protective film 300 on the inner wall of the process chamber 20.

[0117] As one embodiment of the disclosure in this application, an embodiment of this application also discloses a semiconductor process apparatus. Referring to FIG6, the semiconductor process apparatus 200 includes a process chamber 20, an inlet assembly 20A, an upper electrode assembly 20B, a lower electrode assembly 20C, and a controller (not shown in FIG6). The controller includes at least one processor and at least one memory, the memory storing a computer program, which, when executed by the processor, implements the method for forming a protective film according to any of the above embodiments.

[0118] For example, the controller can be a host computer or a slave computer. The controller can open the valve of the inlet assembly 20A to introduce a corresponding process gas into the process chamber 20; the controller can also control the flow rate of the process gas by controlling the opening degree of the valve of the inlet assembly 20A. The semiconductor process equipment 200 may also include a vacuum assembly 24, and the controller can control the vacuum level inside the process chamber 20 by controlling the vacuum assembly 24 to create a vacuum inside the process chamber 20. The semiconductor process equipment 200 may also include a heating assembly 25, and the controller can control the temperature inside the process chamber 20 by controlling the heating assembly 25 to heat the inside of the process chamber 20.

[0119] The upper electrode assembly 20B includes an RF power supply 21 and a spray assembly 22. The RF power supply 21 may include a first RF power supply and a second RF power supply. The first RF power supply may be a high-frequency RF power supply, and the second RF power supply may be a low-frequency RF power supply. The controller is also used to control the RF power supply 21 to provide upper electrode power to the spray assembly 22 to excite the process gas inside the process chamber 20 to generate plasma 100. The upper electrode assembly 20B may also include a matching unit 26, through which the RF power supply 21 provides upper electrode power to the spray assembly 22 to ensure maximum RF power feed. The matching unit 26 may include a first matching unit and a second matching unit, through which the first RF power supply and the second RF power supply respectively provide upper electrode power to the spray assembly 22.

[0120] The lower electrode assembly 20C includes a wafer carrier 23, which can be grounded. The wafer carrier 23 can be, for example, an electrostatic chuck, a mechanical chuck, or a vacuum adsorption chuck.

[0121] The semiconductor process equipment 200 disclosed in this application embodiment may be a high-density plasma chemical vapor deposition equipment or a plasma-enhanced chemical vapor deposition equipment.

[0122] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0123] The above embodiments are merely illustrative of several implementation methods described in detail, but they should not be construed as limiting the scope of the solutions disclosed in this specification. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this specification, and these all fall within the scope of protection of this specification. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method of forming a protective film, characterized by, The method comprises: depositing a first protective film on the inner wall of the process chamber; depositing a second protective film on the surface of the first protective film; wherein the material of the second protective film is different from the material of the first protective film, and the density and smoothness of the second protective film are greater than the density and smoothness of the first protective film.

2. The method of claim 1, wherein, The second protective film comprises a nitrogen-doped silicon carbide film, and / or the first protective film comprises a silicon oxide film.

3. The method of claim 1, wherein, The thickness of the second protective film is less than the thickness of the first protective film.

4. The method of claim 3, wherein, the thickness of the first protective film is greater than or equal to and / or the thickness of the second protective film is less than or equal to 5. The method of claim 2, wherein, When the first protective film is deposited on the inner wall of the process chamber, a first process gas is introduced into the process chamber, the first process gas comprising a first reaction gas and a second reaction gas, the first reaction gas comprising a gas containing oxygen elements, and the second reaction gas comprising a gas containing silicon elements; and / or, when the second protective film is deposited on the surface of the first protective film, a second process gas is introduced into the process chamber, the second process gas comprising a third reaction gas and a fourth reaction gas, the third reaction gas comprising a gas containing nitrogen elements, and the fourth reaction gas comprising a carbon-silicon type gas.

6. The method of claim 5, wherein, When the first reaction gas and the second reaction gas are simultaneously introduced into the process chamber for a first predetermined time, a first radio frequency power source is controlled to be turned on to apply a first radio frequency power to the inside of the process chamber; and / or, when the third reaction gas and the fourth reaction gas are simultaneously introduced into the process chamber for a second predetermined time, the first radio frequency power source and a second radio frequency power source are controlled to be turned on to apply a second radio frequency power and a third radio frequency power to the inside of the process chamber, respectively, and the frequency of the radio frequency signal output by the first radio frequency power source is higher than the frequency of the radio frequency signal output by the second radio frequency power source.

7. The method of claim 6, wherein, After the deposition of the second protective film is completed and before the first radio frequency power source and the second radio frequency power source are turned off, the method further comprises: controlling the first radio frequency power source to apply a fourth radio frequency power to the inside of the process chamber, the fourth radio frequency power being less than the second radio frequency power.

8. The method according to any one of claims 5 to 7, characterized in that, When the first process gas is introduced into the process chamber, the first reaction gas is introduced into the process chamber, and when a third predetermined time is reached, the second reaction gas is started to be introduced into the process chamber; and / or, when the second process gas is introduced into the process chamber, the third reaction gas is introduced into the process chamber, and when a fourth predetermined time is reached, the fourth reaction gas is started to be introduced into the process chamber.

9. A protective film characterized by comprising: The protective film comprises a first protective film and a second protective film arranged in sequence in the thickness direction of the inner wall of the process chamber; wherein the material of the second protective film is different from the material of the first protective film, and the density and smoothness of the second protective film are greater than the density and smoothness of the first protective film.

10. The protective film according to claim 9, characterized by The second protective film comprises a nitrogen-doped silicon carbide film, and / or the first protective film comprises a silicon oxide film.

11. The protective film according to claim 9, characterized by The thickness of the second protective film is less than the thickness of the first protective film.

12. The protective film according to claim 11, characterized in that, the thickness of the first protective film is greater than or equal to and / or the thickness of the second protective film is less than or equal to 13. A semiconductor process apparatus, characterized by, The method comprises: A process chamber, a gas inlet assembly, an upper electrode assembly, a lower electrode assembly, and a controller including at least one processor and at least one memory having a computer program stored therein, the computer program, when executed by the processor, implements the method of forming a protective film according to any one of claims 1 to 8.

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